Historically, the concrete forming industry has generally relied on form/support systems that remain in place until the concrete has attained sufficient strength to support itself and construction loads applied from above. Depending on construction codes applicable to the jurisdiction in which construction is underway, the complete forming system may be required to remain in place up to seven days.
An alternative to the above that is sometimes utilized is generally referred to as a “drop head” system. This type of system allows removal of form components without disturbing the slab supporting components. Drop head systems invariably rely on the use of a support component (shore) and a beam to receive and support the form panels. However, in the past, geometry constraints inherent to these systems required the form panels be smaller in length and width than the spacing of the support posts (shores). Otherwise the panels could not be removed, as they needed to be passed between the supporting posts.
Attempts to overcome this deficiency include U.S. Pat. No. 5,614,122 to Schworer and U.S. Pat. No. 1,907,877 to Roos. These references both teach a drop head system onto which a beam or panel can be mounted, thus allowing beam or panel widths equivalent to the spacing of shore posts. The Roos reference is particularly significant in that the inventor appears to have set about to accomplish the same objectives as the present invention. However, Roos teaches the use of very different components that result in a system with reduced utility.
Specifically, neither of the above references addresses certain practical considerations that should be satisfied to allow maximum utilization of the advantages drop head systems provide. Such practical considerations include providing a means to conveniently accommodate changes in the thickness of the slab, a means to conveniently accommodate slab dimensions that are not exact multiples of standard panel sizes, a means to safely and conveniently erect and dismantle cantilevered slab edge form panels from below by rotation of the form panels, a means to attach form panels to walls to gain support and stability, and a means to remotely release the drop head.
Present concrete slab form systems sometimes use telescopic beams to support forms and form plywood over openings that cannot be filled by standard panels. However, one problem with these telescopic beams is that they tend to deflect excessively at mid span due to the clearances that must be built into the assemblies to permit telescopic action. Mechanical compensating devices are often provided to overcome this deficiency. This requires appropriate adjustment by the crews using them, creating extra cost and labor.
A further problem with current telescopic beams is that they do not present a completely flush upper surface to receive form plywood or panels. This occurs because the telescopic action is provided by one member sliding into a second member, creating a difference in height of the upper surface equal to the thickness of the outer member. Correction of this deficiency can be accomplished by adding shims, which involves added time and labor.
A further deficiency with existing drop head systems is the accommodation of various slab thicknesses. It is common practice to leave the problem of changes in slab thickness up to the contractor to solve on site. This contractor typically has carpenters build single use forms in the areas affected, significantly impacting productivity, material cost, and labor cost.
Another shortcoming of existing systems is that form panels can be dislodged from the supporting shores by strong winds with disastrous results. These systems do not provide a means of positively tying all panels and support posts together in respect to horizontal displacement. Individual or multiple panels can be blown off the supporting shores, creating potential for harm to workers or damage to equipment.
To compensate for this deficiency, a number of stabilizing connections to fixed anchor points are generally installed, thereby holding the form panels in place. Canadian Patent No. 1 172 057 to Young teaches one such system. This again requires additional labor and equipment.
Another shortcoming of present drop head systems is that they usually require the application of hammer blows to remove wedges or to rotate drop bushings. This feature requires a workman to climb up close to the top of the support post, which in some cases can be 12-14 ft. (approximately 3.5-4.5 meters) above the slab that he is working from. This effort is time consuming and tiring that leads to reduced productivity.
In general, wedges employed in drop head systems must have relatively low slopes. Otherwise they could self-release when the supported concrete is being vibrated to remove air from the concrete mix. This low slope requires the use of a long wedge and considerable driving force to release the wedge under the weight of the concrete. Also, the significant extension of the wedge beyond the perimeter of the supporting post when it is released often interferes with the removal of form panels. Some prior art clearly describes the considerable complexity some inventors have resorted to remedy this problem. U.S. Pat. No. 4,147,321 to Gostling is a good example.
Even though wedges are commonly used as load release devices in concrete support posts (shores) they are not the only means employed. U.S. Pat. No. 4,752,057 to Hagemes, and assigned to Hunnebeck, and Canadian Patent No. 2,138,795 to Jackson are examples of other approaches used to provide a quick release. One skilled in the art will easily recognized that these quick release devices require a considerable driving force to overcome the friction that is present to effect release as is the case with wedges. They both include the additional deficiency that at a point in their operating cycle the full supported concrete load is applied to a very small area, resulting in high wear and structural damage of the components.
U.S. Pat. No. 1,907,877 to Roos does not provide a remote means to release the panels, nor does it provide a means to safely hang and erect panels from below. This later deficiency is significant to the user. This reference presents a safety risk when the panel supports are rotated out of the way. At this point the panel is free to fall onto the workers below.
Further, in Roos, considerable cost is incurred to manufacture four wedge assemblies per post and considerable worker effort is expended to set and remove the four loose (chained) wedges located at the top of each support post.
U.S. Pat. No. 5,614,122 to Schworer and assigned to Peri requires use of an additional member, a panel support beam. The use of this member increases the system cost and the labor required to apply the system. The form panels are smaller than the nominal spacing of the support posts (this limitation is required to effect removal of the panels between the support posts). The use of a panel support beam and the use of panels smaller than support post spacing increase the number of components that are required to be handled by the workmen and negatively impact the concrete surface quality due to the long length of components interfaces that produce a visible mark in the surface of the concrete. Schworer does teach a means to remotely operate the “fall collar” that is located near the top of the supporting post and identified in the description of FIG. 9. Workmen are therefore required to use devices to climb up to the drop head when removing panels, as is the case with Roos.
A further deficiency in the prior art involves edges of slabs that cantilever out beyond supporting walls or columns. These edges challenge the form designer to provide a convenient and safe means of erecting and dismantling these forms. The form must extend beyond the edge to be formed in order to provide workers with a place to stand when pouring the concrete. Existing solutions are less than satisfactory to users due to component complexity and the potential exposure to accidental falls experienced by workmen.
A further deficiency in the prior art is that lateral stability of the completed, or partially completed, form assemblies is usually provided by the use of support posts (shores) fitted at the bottom with a three-legged assembly (tripod). These means do not provide sufficient stability to withstand high winds or accidental impact by equipment.